Elastomers are commercially produced by two processes: solution and suspension. It is well known that the crumb form of these conventional elastomers or synthetic rubbers produced in solution or suspension processes are sticky and uneconomical to handle in a continuous bulk materials handling system. Since these elastomers are tacky, when these elastomeric materials are formed into pellets, the pellets usually agglomerate over time or standing such as in shipping and storage. This agglomeration or sticking together over time of the pellets destroys the free-flowing nature of the rubbery polymer making it difficult to handle and process. In fact, the rubbery elastomeric materials are normally compacted into bales and handled manually piece-wise.
In the past attempts to overcome the agglomeration problem associated with pellets of rubber polymers have resulted in the pellets being coated with a fused resinous partitioning agent such as polystryene, polymethylmethacrylate, polyacrylonitrile, polyvinylchloride, or polyethylene. However, these dry powders have a tendency to settle out during coating. And, for some end use applications the presence of these agents cannot be tolerated. More recently, U.S. Pat. No. 5,738,941 coats rubbery polymers or elastomers by coating them with a wax.
Recently, gas phase processes for the production of elastomers have been developed by using inert particulate materials (carbon black, silica, clay, talc, and mixtures of them) in the gas phase process to maintain a fluidized bed and to render the sticky polymer non-sticky. Gas phase elastomers, containing a shell composed mostly of inert particulate material and a core composed mostly of polymer, offer an improvement over conventional rubbers in that they are less sticky, do not require baling, and, thus, can be handled in bulk in their granular, free-flowing form. However, elastomeric particles produced in gas phase processes in the presence of inert particulate materials such as carbon black can have fines and/or dust associated with them. The fines are troublesome in post reaction handling and are a nuisance in finished article fabrication steps.
For elastomers produced in conventional solution and suspension processes there is a need for an alternative to baling or pellets that agglomerate. And for gas phase produced elastomers there is a need to handle the fines associated with them to reduce or eliminate post-handling problems. Therefore, the present invention provides a method for pelletizing elastomers which are typically baled and a method for incorporating fines into gas phase elastomers by pelletizing.